1. Field of the Invention
This invention relates to relay apparatus. In particular, it relates to electromagnetically actuated switches used in relay apparatus.
2. Description of the Prior Art
Sealed contact switches are well known in the Electronic and Communication Industry and have found extensive application in electrical systems performing a wide range of switching functions. A typical switch comprises a pair of reed members or pole-pieces and a stem-armature assembly suspended at their ends by an envelope member, usually glass, such that an armature of the stem-armature assembly overlaps contact surfaces of the pole-pieces. A relay is constructed utilizing a switch such that an electrical winding encircling the envelope member generates a magnetic field for actuating the armature of the switch to engage and disengage contact surfaces of the pole-piece members and thereby control an external electrical circuit connected with the relay. Such switches, serve well in particular circuit applications; however, the irregular surface character of the pole-piece contacts and stem armature reduces the areas of contact upon engagement and renders the switch essentially current limited in that current of a magnitude beyond a predetermined value tends to cause melting of the irregular contact surfaces which increases the tendency of the pole-piece contact and armature to stick together in a closed position.
The current carrying capacities of such switches may be increased by the employment of the well-known mercury-wetted type of switches. Typically, mercury wetted surfaces enable an electrical connection to be uniformly established over the entire surface of the contacts. In such a switch, a pool of mercury located in one end of the envelope moves by capillary action over the stem and armature to wet the contact surfaces of the armature and pole-pieces and thereby increase the current capacity of the switch. A problem occurs with this type of mercury switch in that it is position sensitive. If the switch is mounted in one position, the pool of mercury will shift thereby shorting the reed members or the stemarmature and pole-piece contact surfaces together rendering the switch inoperable. If the switch is mounted in another position, the pool of mercury may be shifted to a location within the switch away from the reed members and from the stem-armature and pole-piece assemblies thereby creating dry contacts that result in a lower current carrying capacity of the switch.
Accordingly, a need exists for a multipositional mercury switch that may be mounted in any position in electrical and electronic equipment.